Patients in hospital Intensive Care Units (ICU) may experience impairment in their ability to breathe volitionally due to their underlying disease condition and require positive pressure mechanical ventilation (PPMV) to provide ventilatory assistance. PPMV is routinely used in combination with sedation in the ICU to provide artificial ventilation for these critically ill individuals. Additionally, many patients undergoing surgery under general anesthesia, for example in hospital Operating Rooms (OR), or procedures under anesthesia or sedation, for example in hospital Emergency Rooms (ER), commonly require PPMV for ventilatory assistance while anesthetized or sedated.
Although mechanical ventilation is a life-sustaining modality, when combined with sedation or anesthesia it interferes with active contraction of the diaphragm. Prolonged totally controlled mechanical ventilation can result in the complete absence of neural activation and mechanical activity of the diaphragm and has been shown to induce muscle atrophy, proteolysis, and reactive oxygen species liberation, leading to rapid loses in diaphragmatic function, a syndrome known as Ventilator-Induced Diaphragmatic Dysfunction (VIDD).
The onset of diaphragm disuse atrophy is rapid, leading to slower patient recovery, which often results in ventilator dependence and translates into higher incidence of ventilator-acquired pneumonia and nosocomial infections, longer stays in the ICU, and escalating hospitalization costs.
In addition to ICU patients, mechanical ventilation is the primary modality of ventilatory assistance for individuals with disease conditions that adversely affect neurological function, such as Spinal Cord Injury (SCI). These individuals may experience impairment in their ability to breathe volitionally due to partial or complete loss of control of the diaphragm, and are prone to lifelong dependence on a mechanical ventilator.
Several viable alternatives to PPMV for assisting breathing are currently available, and have been indicated for use in patients requiring long-term ventilatory assistance such as Spinal Cord Injury (SCI) patients or patients with Congenital Central Hypoventilation Syndrome (CCHS). They include phrenic nerve stimulation and diaphragmatic pacing. These methods use electrical stimulation to induce contraction of the diaphragm using an electrode and an external pacing control box or an implanted pacemaker device.
The two phrenic nerves, which control activation of the diaphragm, run through the thorax, along the left and right sides of the heart, and then to the diaphragm. Phrenic nerve stimulation is performed by electrically stimulating the phrenic nerve to control the patient's diaphragm, which may induce a respiratory cycle. Conventional techniques include surgically implanting a nerve cuff around the phrenic nerve (at the neck or chest level), and then delivering an electrical stimulus from an externally located controller through the cuff to the phrenic nerve. This procedure is quite invasive, requiring incisions when deploying the nerve cuffs, and quite expensive, so it is only selectively used in patients with a life-long requirement for assisted ventilation. In addition, the direct placement of the nerve cuffs around the phrenic nerves may damage the phrenic nerves. These phrenic nerve stimulation systems have not heretofore been prescribed for temporary use in critically ill ICU patients.
Other phrenic nerve stimulation techniques are known, such as that described in U.S. Pat. No. 8,195,297. However, the system disclosed in the '297 patent does not allow for rapid, short term use in an ICU environment for the management of ICU patients particularly in the first few days after start of PPMV.
Another method for electrically stimulating the diaphragm is known as diaphragmatic pacing. Conventionally, diaphragmatic pacing is performed by laparoscopically implanting four electrodes directly on the diaphragm (two on each side), with electrical leads connected to a controller residing external to the body. Conventional diaphragmatic pacing procedures are also quite time consuming and relatively invasive, requiring incisions during implantation, presenting risk during the implantation procedure and risk of chronic infection at the lead entrance sites to the body. Accordingly, these diaphragmatic pacing systems have not heretofore been prescribed for temporary use in critically ill ICU patients.
One such diaphragmatic pacing system is described in U.S. Pat. No. 7,962,215. In addition to being surgically demanding, the diaphragmatic pacing system of the '215 patent is employed to administer therapy to convert Type IIa (fast-type) muscle fibers to Type I (slow-type) muscle fibers in patients who have been ventilated for prolonged periods, whose muscle fibers have all atrophied and converted to Fast-type (VIDD). The therapy described in the '215 patent, however, will not be desirable in the treatment of critical care patients that still have both Type IIa (fast-type) muscle fibers and Type I (slow-type) and will need to have both types to successfully wean off of PPMV.
Accordingly, there exists a need for minimally invasive diaphragm pacing systems and methods for rapid, short term use, as appropriate in the ICU environment, for the management of ICU patients particularly in the first few days or weeks after start of PPMV.